When opto-electronic devices and components are to be connected to each other, such as an optical emitter or receiver to an optical fiber, the devices must be precisely aligned in order for the overall assembly to operate properly. For example, the optical axis of an emitter, such as a semiconductor laser, must be precisely aligned with that of the optical fiber, so that a laser beam emitted from the semiconductor laser enters the optical fiber properly. Standard tolerances for the precision of such alignment range from ±25 μm to ±1 μm. Accordingly, alignment is widely recognized as the most expensive phase of assembling optical packages and often represents 25-50% of packaging costs.
Two methods of aligning optical devices are well known in the art. In “active alignment,” one optical device (typically the emitter) is turned on during the alignment process. The light beam emanating from the emitter passes through the fiber and is detected by a photodetector at the other end of the fiber. Relative movement between the emitter and the optical fiber is imparted until the photodetector detects a high or maximum light intensity, which indicates a desirable alignment between the optical fiber and the emitter. A similar process can be used to in aligning an optical fiber and a photodetector, in which relative movement between the optical fiber and the photodetector is imparted until satisfactory alignment is achieved. This trial-and-error method of active alignment requires the optical devices to be connected into an operational circuit during the packaging process, is time-consuming and results in high fabrication costs.
In “passive alignment,” optical devices need not be on to set the alignment, and advantage can be taken of alignment markers created during manufacturing of the devices to be aligned. However, in order to meet today's stringent alignment tolerances, expensive machine vision and 6-axis robotics are typically employed, and the process remains cumbersome and expensive.
As the data rates of computing backplanes (and consumer products such as video and mobile devices connecting to the backplanes) continue to increase, optical interconnections are expected to be preferred over copper lines. Therefore, there is a need for a low-cost, passive optical alignment method.